Stabilization of lubricants



3,011,976 Federated Dec. 5, 1961 has 3,011,976 STABILIZATION F LUBRICANTS Henry A. Cyba, Chicago, and Robert H. Rosenwald,

Western Springs, Ill, assignors to Universal Oil Products Company, Des Piaines, 1th., a corporation of Delaware No Drawing. Filed July 13, 1959, Ser. No. 826,441 16 Claims. (Cl. 252-32) This invention relates to the stabilization of lubricants and more particularly to the use of improved inhibitors for efiecting the stabilization of lubricants.

In recent years, stringent requirements for lubricants in certain applications have resulted in the availability of a new class of lubricants referred to in the art as synthetic lubricants. These lubricants do not necessarily replace petroleum oils in conventional usage, but are designed for special applications where the petroleum oils do not. function to a satisfactory degree. These synthetic lubricants have found particular use in Winter-grade crankcase oils, turbo-engine oils, aviation instruments, automatic weapons, etc. For example, aircraft gas turbines require oils capable of providing satisfactory lubrication at temperatures ranging as low as -65 F. and as high as 275 F. during use. Temperatures up to 500 F. are encountered for intervals of from one to two hours during shut-down. Petroleum lubricants are unsatisfactory at high altitudes or in the Winter season for use in machine guns and automatic cannons which frequently could not be made to fire because of congealed lubricants. Because they are used under such stringent conditions, the synthetic lubricants undergo undesirable deterioration including, for example, formation of deposits, discoloration, change of viscosity, etc. While the features of the present invention are particularly applicable to the stabilization of synthetic lubricants, it is understood that they also may be used for the stabilization of petroleum lubricants.

The synthetic lubricants are of varied types including aliphatic esters, polyalkylene oxides, silicones, esters of phosphoric and silicic acids, highly fluorine-substituted hydrocarbons, etc. Of the aliphatic esters, di-(Z-ethylhexyl) sebacate is being used on a comparatively large commercial scale. Other aliphatic esters include dialkyl azelates, dialkyl suberates, dialkyl pimelates, diallcyl adipates, dialkyl glutarates, etc. Specific examples of these esters include clihexyl azelate, di-(Z-ethylhexyl) azelate, bis-(l-methyl cyclohexylmethyl) sebaca-te, di-3,5,5-trimethylhexyl glutarate, di-3,5,S-trimethylpentyl glutarate, di-(Z-ethylhexyl) pimelate, di-(Z-ethylhexl) adipate, triamyl tricarballylate, pentaerythiitol tetracaproate, dipropylene glycol dipelargonate, 1,5-pentanediol-di-(2- ethylhexanonate), etc. The polyalkylene oxides include polyisopropylene oxide, polyisopropylene oxide diether, polyisopropylene oxide diester, etc. The silicones include methyl silicone, methyl-phenyl silicone, chlorophenylsilicone, methylchlorophenylsilicone, etc, and the silicates include, for example, tetraisooctyl silicate, tetrakis-n-dodecyl silane, didodecyldioctyl silane, diphenyl-di-n-dodecyl silane, octadecyltridecyl silane, hexa-Z-ethylhexoxydisiloxane, etc. Various phosphates as tricresyl phos phate, trioctyl phosphate, tris-(chlorophenyl) phosphate, chlorophenylphenyl phosphate also are being used. The highly fluorinated hydrocarbons include fiuorinated oil, perfiuorohydrocarbons, etc, Other synthetic lubricants proposed for use in high temperature service as, for example, jet fuel lubrication, etc., include pentaerythritol esters and trimethylolpropane esters.

The present invention also is applicable to the stabilization of greases made by compositing metallic soaps with the synthetic lubricating oils described above and are referred to herein as synthetic greases. These metal base synthetic greases may be further classified as lithium base synthetic grease, sodium base synthetic grease, calcium base synthetic grease, barium base synthetic grease, strontium base synthetic grease, aluminum basesynthetic grease, etc. These greases are solid or semi-solid gels and, in general, are prepared by the addition to the synthetic lubricating oil of hydrocarbon-soluble metal soaps or salts of higher fatty acids as, for example, lithium stearate, calcium stearate, aluminum naphthenate, etc. The grease also may contain thickening agents such as silica, carbon black, metal oxides, phthalocyanines, polyacrylates, talc, bentone and organo-treated clays, etc. Alkylureas, arylureas, p-tolyl and p-chlorophenylurea derivatives of bitolylendi-isocyanate, pteridines, N-n-octadecylterephthalornate and other organic thickencrs are used. Again, While the present invention is particularly applicable to the stabilization of synthetic grease, the inhibitors also may be used in petroleum base grease.

it is general practice to incorporate w inhibitor in lubricants in order to improve the stability thereof- Because of the severe requirements imposed upon the synthetic lubricants, research continues to search for better inhibitors inorder to further improve the lubricants and permit their use for longer periods of'time in present applications, as Well as to permit their use even under more severe conditions as, for example, in the engines of the future which are being developed to operate at peak eliicieucy at high altitudes. It is important that the lubricant is stable, retains its lubricity properties, does not undergo deposit formation, retains its desirable viscosity, etc. and,

in many applications it is important that the inhibitor also serves to retard and/or prevent corrosion of the metal surfaces with which the lubricant comes into contact. Generally at least a small amount of Water is present, either being formed during combustion and/or entrained in the fuel supplied to the engine. The combination of water and corrosive constituents cause corrosion of the metal. Accordingly, the inhibitor serves an important function in also retarding and/ or preventing such corrosion.

In addition tomeeting the chemical and physical requirements hereinbefore described, the inhibitor must be of sutficiently low cost to be economically acceptable. In other words, regardless of how effective an inhibitor is, if it cannot be marketed at a reasonable price, it will not be accepted in the industry because of economic reasons. Applicants have made a detailed research inyestigation of extensive. classes of chemical compounds which might meet inhibitor requirements and still be marketed at a reasonable cost. As a result of this extensive investigation, applicants have found that certain dianu'nodiphenyl methane compounds meet these requirements provided that the diaminodiphenyl methanes themselves are selected with certain important requirements. These compounds offer advantages over thepreviously used metallic type inhibitors as, for example, zinc dialkyldithiophosphate or other organo metallic com.-

pounds, because the diarninodiphenyl methanes are ash- 1 less in nature and do not introduce metallic components which may contribute to serious difficulties in engine performance such as preignition, rumble, spark plug fouling, combustion chamber deposits, etc. becomes more severe as the compression ratios of engines are raised, with a parallel increase in temperature of the crankcase oil.

As hereinbefore set forth, applicants have found that certain diamino-diphenyl methane compounds, meeting the important requirements to be hereinafter set forth in detail, appear to be particularly desirable for use in the stabilization of lubricants. The use of diaminodiphenyl compounds has been proposed heretofore for use as an additive in lubricating oil and other substrates. I

This problem However, the teachings of the prior art to the use of such compounds are vague and indefinite and include, on an equivalent basis, compounds having a. diaminodiphenyl configuration connected by alkane groups, nitrogens, oxygens, phosphorus, aluminum, boron, antimony, sulfur, etc. In addition, the broad and vague teachings of the prior art include compounds in which these bridging groups and/ or the phenyl nuclei may be substituted by aliphatic, aryl, heterocyclic, halogen or other groups. All of these are placed on an equivalent basis in the prior art teachings and require an extensive investigation, study and analysis in order to determine whether any of these classes of compounds would be suitable for use at the severe conditions required of the lubricants heretofore described. In general these prior art teachings go back many years and certainly before the development of the modern engines as, for example, turbo jet engines, turbo props, gas turbines, free piston turbines, etc. Accordingly, the old prior art was not faced with the problems entailed in the more severe requirements of modern day lubricants and were not directed towards the solution of these problems.

As a result of their extensive investigation, applicants have found that certain of the diaminodiphenyl compounds will meet these requirements, provided that they, in turn, meet other important requirements. For example, applicants have concluded that the diarninodiphenyl compounds having metallic constituents are undesired because of the possible adverse effect on engine performance as hereinbefore set forth. Applicants have ruled out the diaminodiphenyl sulfides because of the possible undesirable corrosion effect due to the use of inhibitors containing sulfur. Also as hereinbefore set forth, it is important that the inhibitor compound is sufiiciently low in cost to be economically acceptable and this in turn has ruled out the diaminodiphenyl ethers because they are more expensive to manufacture. Applicants have concluded that the diaminodiphenyl methanes appear to best meet the requirements hereinbefore set forth and furthermore that only those having the amino groups in the 4,4 positions should be used. 4,4'-diaminodiphenyl methane may be prepared at a lower cost than other diaminodiphenyl methanes in which the amino groups are arranged in different positions on the phenyl nuclei, and accordingly offers a less expensive source for preparing the desired inhibitors.

From the above discussion, it will be seen that applicants have concluded that the 4,4'-diaminodiphenyl methanes appear to meet the desired requirements. However, as further investigation by applicants has shown, the diaminodiphenyl methanes themselves also must meet certain important requirements in order to impart the desired potency to the inhibitor. Accordingly, applicants have discovered, and now are claiming as their invention, the use in lubricants of a diaminodiphenyl methane meeting all of the following requirements:

(1) The diaminodiphenyl methane must contain one or two alkyl groups substituted on each nitrogen atom.

(2) When the inhibitor is a 4,4-di-alkylaminodiphenyl methane, both of the alkyl groups must be of secondary configuration.

(3) When the inhibitor is an N,N,N,N-tetraalkyl- 4,4'-diaminodiphenyl methane, the alkyl groups must be either of secondary configuration or comprise ethyl groups.

(4) When bearing corrosion inhibition is important, the phenyl nuclei must not contain an alkyl substituent in a position ortho to the nitrogen atoms.

As hereinbefore set forth, each of the specific requirements enumerated above are essential, as will be shown by the examples appended to the present specifications. The inhibitor compounds meeting these requirements are efiective inhibitors and may be manufactured at a reasonable cost, thereby offering to the industry an improved inhibitor which may be incorporated into lubricants for use under the severe conditions of modern technology.

In one embodiment the present invention relates to a method of stabilizing a lubricant which comprises incorporating therein a stabilizing concentration of an inhibitor selected from the group consisting of 4,4'-di-(secalkylamino) diphenyl methane, N,N,N',N'-tetra(secalkyl)-4,4-diaminodiphenyl methane and N,N,N,N'- tetra-ethyl-4,4-di-aminodiphenyl methane.

In a specific embodiment the present invention relates to a method of stabilizing lubricating oil and preventing corrosion of metal surfaces contacting said lubricating oil which comprises incorporating in said lubricating oil an inhibitor having antioxidant and corrosion inhibiting properties, said inhibitor being selected from the group consisting of 4,4'-di-(secalkylamino)-diphenyl methane, N,N,N,N'-tetra-(sec-alkyl)-4,4'-diaminodiphenyl methane, and N,N,N,Ntetra-ethyl-4,4-diaminodiphenyl methane, said inhibitor being devoid of alkyl substituents in the positions ortho to the nitrogen atoms.

In another specific embodiment the present invention relates to a method of stabilizing a lubricant which comprises incorporating therein a stabilizing concentration of 4,4'-di-(sec-'butylamino)-diphenyl methane.

In another embodiment the present invention relates to a lubricant containing the inhibitor as herein set forth.

4,4-di-(isopropylamino)-dipheny1 methane, 4,4'-di- (sec-butylamino)diphenyl methane, N,N,N,N'-tetra- (isopropyl)-4,4'-diaminodiphenyl methane, N,N,N',N- tetra-(sec-butyl)-4,4'-diaminodiphenyl methane, and N,N,N',N-tetra-ethyl-4,4-diaminodiphenyl methane are preferred inhibitor compounds for use in the present invention. Other inhibitor compounds meeting the requirements hereinbefore set forth include 4,4-di-(secamylamino)-diphenyl methane, 4,4-di-(sec-hexylamino)- diphenyl methane, 4,4'-di-(sec-heptylamino)-diphenyl methane, 4,4'-di(sec-octylamino)-diphenyl methane, 4,4'-di-(sec-nonylamino)-diphenyl methane, 4,4-di-(secdecylamino)-diphenyl methane, 4,4-di-(sec-undecylamino)- diphenyl methane, 4,4'-di-(sec-dodecylamino)-diphenyl methane, etc., N,N,N',N'-tetra-(sec-amyl)-4,4- diamino-diphenyl methane, N,N,N,N'-tetra-(sec-hexyl)- 4,4'-diaminodiphenyl methane, N,N,N,N'-tetra-(sec-heptyl)4,4'-diaminodiphenyl methane, N,N,N,N'-tetra (sec-octyl)-4,4'-diaminodiphenyl methane, N,N,N',N'- tetra-(sec-nonyl)-4,4-diaminodiphenyl methane, N,N,N', N-tetra-(sec-decyl)-4,4-diaminodiphenyl methane, N,N, N',N'-tetra-(sec-undecyl)-4,4'-diaminodiphenyl methane, N,N,N',N' tetra (sec-dodecyl) 4,4 diaminodiphenyl methane, etc.

In general it is preferred that the alkyl substituents are the same and contain from 3 to about 12 carbon atoms each in the di-alkyl substituted compounds and from 2 to about 12 carbon atoms each in the tetra-alkyl substituted compounds. In some cases, these alkyl groups each may contain a larger number of carbon atoms, although in general should not exceed about 20 carbon atoms each. In still other cases, the substituents attached to the nitrogen atoms, particularly in the tetra-alkyl substituted compounds, may be ditferent but at least one each of the substituents attached to the nitrogen atoms must contain the secondary alkyl group with the exception of the tetraethyl amino substituted compound. While all of these compounds are elfective for the purpose, it must be pointed out that they will not necessarily be equivalent in the same or different substrates.

It has been found that alkyl substituents in the 2,2 positions on the phenyl nuclei do not reduce the potency of the inhibitor but do not appear to increase the potency. Accordingly, there is no objection to the inhibitor compounds containing alkyl substituents in the 2,2 positions. Illustrative compounds in this category include 2,2'-dimethy1-4,4'-di-(sec-butylamino)-diphenyl methane, 2,2- di-ethyl-4,4-di-(sec-butylamino)-diphenyl methane, 2,2- di-propyl-4,4'-di-(sec-butylamino)diphenyl methane, 2,2-

di-sec-butyl-4,4'-di-(sec-butylamino)-diphenyl methane, etc.

As another example of the complexity in this inhibitor problem, in contrast to the indifierent efiect of substitutions in the 2,2 positions, it has been found that substitutions in the 3,3 positions (positions ortho to the nitrogen atoms) seriously aiIect the bearing corrosion in hibitor property of the additive. Accordingly, when this property is important as, for example, when incorporated,

in lubricating oil for use in automobile engines, diesel engines, stationary engines, etc., the inhibitor compound must be devoid of alkyl substituents in the 3,3 positions. This will be illustrated further in the examples appended to the present specifications.

The inhibitor for use in the present invention may be prepared in any suitable manner. Diaminodiphenyl methane is available commercially or may be prepared in any suitable manner as, for example, by the reaction of aniline with formaldehyde in the presence of an acid. Diaminodiphenyl methane then is reductively alkylated with the esired ketone in the presence of a suitable catalyst to produce either the dior tetra-substituted derivative. Any suitable catalyst may be used in the reductive alkylation including those containing platinum, palladium, cobalt, nickel, molybdenum, etc. Another catalyst used for this reaction is a mixture of the oxides of chromium, copper and barium. In general the reaction is effected at an elevated temperature of from about 200 to about 500 F. and a hydrogen pressure of from about 50 to about 2000 pounds per square inch or more. For example, 4,4-di(sec-butylamino)-diphenyl methane is prepared by the reductive alkylation of 4,4"-diaminodiph'enyl methane with methylethyl ketone. When the isopropyl derivative is desired, acetone is used as the alkylating agent. 4,4.'-di-(l-methylheptylamino)-diphenyl methane is pre pared by the reductive alkylation of 4,4'-diarninodiphenyl methane with methyl he-xyl ketone. 4,4'-di-(1-ethyl- 3-rnethylpentylamino)-diphenyl methane is prepared by the reductive alkylation of 4,4'-diaminodiphenyl methane with ethylisoamyl ketone. When the tetra-alkyl substituted compounds are desired, the ketone is reacted in the inhibitor may be added to one or more the components of the grease before final compositing thereof. When desired, the inhibitor may be prepared as a solution in a suitable solvent including, for example, aromatic hydrocarbons such as benzene, toluene, xylene, ethyl benzene, cumene, decalin, etc., or mixtures such as naphtha, kerosene, lube oil, etc.

It is understood that the inhibitor may be used along with other additives incorporated in the lubricant. For example, a metal deactivator, dye, viscosity index improver, pour point depressant, anti-foaming additive, lubricity and extreme pressure additive, anti-scufiing additive, detergent, etc, may be incorporated in the lubricant. When desired, the inhibitor of the present inven tion may be prepared as a mixture with one or more of these other additives and incorporated in this manner in the lubricant.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

The data reported in Examples 1, II and III were obtained in a Lauson engine operated at high oil temperature (280 F.) and low jacket temperature (210 F.). Each test was conducted for 115 hours. A typical commercial paraifinic solvent-extracted lubricating oil was used. It has been found that the Lauson engine results correlate with the results obtained in the Chevrolet L-4 tests and accordingly properly evaluate the difierent additives.

EXAMPLE I As hereinbefore set forth, the diaminodiphenyl methane must contain at least one or two alkyl groups attached to each nitrogen atom. When the inhibitor is a 4,4-di- (alkylamino)-diphenyl methane, the alkyl substituents must be of secondary configuration. This is shown in the following table which compares the results of tests conducted with ditferent samples of the lubricant containing diferent additives. Each of the additives was employed in a concentration of 0.5% by weight of the lubricating Run No. Additive Noneoil before testing Noneoil after testing 4,4'-dlaminodiphenyl methane.

2,2-di-met11yl-4,4-diaruino-diphenyl urethane. 3,3-di-lsopr0py1-4,4-diamino-diphenyl methane 3,3-di-sec-butyl-4,4-diamino-diphenyl methane 4,4-di-(meth ylamino)diphonyl methane. 4,4"di-(ethylamino)-di henyl methane 4,4-di-(n-propylamino ,-dipheny1 methane" 4,4-dl-(isopropylamino)-diphenyl methane 4,4J-di-(n-butylamin0)-diphenyl methane. 4,4-di-(sec-butylammo)-dipheny1 methane.

4,4-di-(3-penty1amiu0)-diphenyl methane oil. For comparative purposes, a sample of the oil without additive is included in the table.

Table l Usedoil analysis Bearing weight Neutrali- Pentane Viscosity, SSU

loss, zation insoluble, grams number weight;

Mg. percent 100 F. 210 F. KOH/g.

0.01 Nil 359 55. 6 10. 78 5.16 742 74. 7

1 Not soluble in the oil.

twice the proportions reacted in the preparation of the di-alkyl derivatives.

The inhibitor will be used in the substrate in an amount sufiicient to obtain the desired stabilization and, when desired, bearing corrosion inhibition. In general this concentration will be within the range of from about 0.01% to about 5% and preferably of from about 0.1% to about 3% by weight of the lubricant. The inhibitor is added to the lubricant in any suitable manner and prefer: ably with intimate mixing in order to obtain uniform distribution of the inhibitor in the lubricant. In some cases the inhibitor may be added to the lubricant during the manufacture thereof as, for example, when used in grease From the data in the above table, it will be noted that the lubricating oil after evaluation in the Lauson engine underwent a bearing weight loss of almost three grams, an increase in neutralization number to above ten, anincrease in pentane insoluble material to over 5 percent,'and almost double increase in viscosity (compare run number 2 with run number 1).

As h'ereinbefore set forth, the diaminodiphenyl methane must contain certain alkyl substituents attached to the nitrogen atoms. Thus, it will be noted that diaminodiphenyl methane (run number 3) was not soluble in the oil and accordingly is of no use for the purpose and obviously could be evaluated in the Lauson engine. Even when substituted with di-methyl groups attached to the phenyl nuclei (run number 4) or methyl groups attached to the nitrogen atoms (run number 7), the compounds were not soluble in the oil. When substituted with diisopropyl groups attached to the phenyl nuclei, the compound was soluble in the oil (run number 5) but it will be noted that the lubricating oil induced a bearing weight loss of almost two grams and also had a comparatively high viscosity. Similarly, when substituted with sec-butyl groups on the phenyl nuclei (run number 6), the lubricating oil containing this additive induced a bearing weight loss of 2.4 grams and similarly resulted in a comparatively high viscosity. Accordingly, it will be seen that the substitution of the alkyl groups on the phenyl nuclei, whether methylethyl, propyl or butyl, even though the latter two are of secondary configuration, was not efiective in serving as a weight bearing corrosion inhibitor or in inhibiting deterioration of the oil as indicated by the comparatively high viscosity, neutralization numbers and pentane insolubles.

As hereinbefore set forth, the alkyl substituents must be attached to the nitrogen atoms and must be of secondary configuration in the dialkylated derivatives. This is clearly illustrated by comparing run number 9 with the oil containing 4,4'-di (sec-butylamino) diphenyl methane (run number 12) induced very small bearing weight loss of only 0.0018 gram, a low neutralization number and pentane insolubles, and also resulted in an oil of substantially the same viscosity as the original oil.

These data show the important requirement that, not only must the diaminodiphenyl methane contain alkyl groups and the alltyl groups must be attached to the nitrogen atoms, but also that the alkyl groups must be of secondary configuration in the dialkylated compounds. Run number 13 illustrates an additional dialkylated compound in which the alkyl substituents are of secondary configuration and are attached to the nitrogen atoms.

EXAMPLE II As hereinbefore set forth, in the 4,4'-di-(sec-alkylamino)-diphenyl methanes, alkyl groups in the 2,2 positions are of substantially no effect, whereas alkyl substitutions in the 3,3 positions (ortho to the nitrogen atoms) adversely aifect the bearing corrosion inhibitor properties. This is illustrated in Table II. These data were obtained in the manner described in Example I. For ready comparison, run numbers 10 and 12 are repeated in this table.

Table 11 Used oil analysis Bearing Run No. Additive weight Neutrali- Pentane Viscosity, SSU

loss, zution insoluble, grams number weight Mg. percent 100 F. 210 F. KOH/g.

. 4,4-di-(sec-butylarnino)-diphenyl methane 0.0018 0. 15 0. 10 308 56. 1 2,2'-dimethyl-4,4-di-(sec-butylarnino)-diphenyl methane 0. 0054 0. 0. 28 360 55. 4 3,3-dimethyl-4,4'-di-(sec-butylamino)-dipheny1 methane 2. 0290 5.10 1. 04 605 67. 5 r 4,4-di-(isopropylamino)-diphenyl methane 0.0092 0.12 0. 10 867 56. 1 3,3'-dimethyl-4,4-di-(isopropylamino)-dipheny1 methane 2 0825 4. 90 1. 32 535 64.6

run number 10 and run number 11 with run number 12. It will be noted that the normal .propyl derivative was of comparatively small benefit in that the bearing weight loss was still above 0.8 gram and the viscosities were 491 and 62 seconds. In contrast, in run number 10, using 4,4'-d.i(isopropylamino) diphenyl methane, the bearing weight loss induced by the lubricating oil containing this additive was only 0.0092 and the neutralization number 0.1 2, the pentane insolubles only 0.1% and the viscosity substantially the same as the original oil (run number 1). Thus it will be seen that this compound was extremely effective, both in inhibiting bearing corrosion and in stabilizing the oil, so that the used oil retained substantially the same properties as the original oil.

This same benefit is evidenced by comparing run number 12 with run number 11. In run number 11, in which the alkyl substituent is of normal configuration, the oil containing this inhibitor induced considerable bearing corrosion (2.726 grams loss) and also resulted in considerable deterioration of the oil as evidenced by the neutralization number and high viscosity. In contrast,

From the data in the above table, it will be seen, from a comparison of runs 12 and 14, that substitution of methyl groups in the 2,2 positions did not considerably affect the inhibiting properties of the 4,4'-di-(sec-butylamino)-diphenyl methane. In contrast, from a comparison of run 12 with run 15, it will be noted that the methyl substituents in the 3,3 positions increases the amount of bearing weight loss from 0.0018 to 2.0290 grams, increases the neutralization number from 0.15 to 5.10, and the pentane insolubles from 0.10% to 1.04%. A similar effect is noted by comparing run number 10 with run number 16 as applied to the 4,4-di-(isopropylamino)-diphenyl methane.

EXAMPLE III .As hereinbefore set forth, when the inhibitor compound in N,N,N',N'-tetra-alkyl substituted, the alkyl groups maybe either of secondary configuration or may comprise ethyl groups. This is illustrated by the data in the following table, which were obtained in the manner described in Example I.

Table III Used oil analysis Bearing Rim No. Additive weight Neutrali- Pentane Viscosity, S51) 55, zation insoluble, grams number weight Mg. percent 100 F. 210 F. KOH/g.

17 N,N,N',N-tetra-methyl-4,4'-diaminodiphenyl methane. 2. 3016 7. 3 0. 649 69. 18 N ,N,N,N-tetra-ethyl-4,4-diaminodiphenyl methane.--" 0.0328 0. 24 0.57 370 56.2 19 N,N,N' ,N'-tetra-(n-propyl) 4,4 -diaminodipheny1 methane 2. 9599 0. 82 2. 77 626 69. 7 20 N,N,N',N-tetra-(isopropy1)-4,-1-diaminodiphenyl methsne 0. 0358 0. 15 0. 32 361 55. 9

From a comparison of run 18 with run 17, it will be noted that the tetra-ethyl derivative was eifective in reducing the bearing weight loss and in stabilizing the other properties of the lubricating oil, whereas the tetra-methyl derivative was not effective for this purpose, resulting in an oil inducing a bearing weight loss of over two grams EXAMPLE v The lubricating oil used in this example was a syn-v thetic oil, more particularly dioctyl sebacate, marketed under the trade name of Plexol 201. The oil was evaluated in accordance with an Oxygen Stability Test in which a 100 cc. sample of the lubricating oil is placed in a bath maintained at 400 F. and air is blown therethrough at a rate of 5 liters of air per hour. The sample of lubricating oil is examined periodically and the time to reach an acid number of 5 is reported. It is apparent that the longer the time required to reach an acid number of 5 the more stable is the sample of lubricating oil. In othher words, it takes longer for the more stable oil to deteriorate.

The data are reported in the following table and include results obtained with a sample of the lubricating oil without additive and samples containing dilferent additives, including those comprised within the present invention an dthose outside of the scope of the present invention. When employed, the additive in all cases was used in a concentration of 0.0033 mole per 100 cc. of lubricating oil. This is approximately 1% by weight thereof.

Table IV Hours to Run Additive acid N 0. number None 9 3,3-di-{isopropyl)-4,4-diaminodiphenyl methane 21 4,4-di-(n-propylamino)-diphenyl methane. 24 4,4-di-(ispr0pylamin0)-diphenyl methane 41 25 3,3-(ll-(sec-butyl)-4,4-diaminodiphenyl methane. 22 26 4,4-di-(n-butylamino)-diphenyl methane 23 27--- 4,4-di-(sec-buty1amino)-diphenyl methane 42 28 4,4-di-(3pentylamlno)-diphenyl methane 43 It will be noted that the data in the above table confirms the critical importance of utilizing a diaminodiphenyl methane in which secondary alkyl groups are attached to the nitrogen atoms. It will be noted that run members 22 and 25, in which the secondary alkyl groups are attached to the phenyl nuclei and run numbers 23 and 26 in which the alkyl groups attached to the nitrogen atoms are of normal configuration, all resulted in stabilities of about one-half of those obtained in run numbers 24, 27 and 28 in which the alkyl substituents are of secondary configuration and are attached to the nitrogen atoms.

EXAMPLE V As hereinbefore set forth, where bearing corrosion inhibiting properties are not of importance, the inhibitor also may contain alkyl substituents in the 3,3 positions. Also, as hereinbefore set forth, such substitutions in the 2,2 positions are of minor effect. This is illustrated by the data in the following table. For ready reference run numbers 24 and 27 of Table IV are repeated in the following table. The data reported in this table were obtained in the same manner as described in Table IV.

Table V Hours to Run Additive no N 0. number of 5 i 24. 4,4fdi-(lsopropylamino) -diphenyl methane 41 29. 3,3 dl-methyl -4,4 -di (isopropylamino) diphenyl 45 methane. 27." 4,4-di-(see-butylamino)-dlphe11yl methane 42 30. 2,2 di-methy1v4,4- di- (secybutylamino) diphenyl 43 methane. 31. 3,3 di-rnetl1yl-4,4 -di- (sec -butylarnino) -diphenyl 46 methane. 32-. 3,3 ,6,6-tetra -methyl-4,4 -di- (sec-butylamino) -dl- 39 I phcnyl methane.

EXAMPLE VI A similar series of runs were conducted in the same manner as Examples IV and V for the purpose of evaluating the tetra-alkylated derivatives. The substrate was Plexol 201 and the concentration of additives and other conditions of evaluation were the same as described in Example IV. These results are reported in the following table.

Table VI Hours to Run Additive fiQid No. number 33 N,N,N,N tetra -xnethyl 4,4 diamino diphenyl l8 methane. 34"." N,N,N,N tetra ethyl 4,4 diarnlno diphenyl 31 methane. 35 N,N,N.N-tctra (n-propyl) -4,4-diamlno-diphenyl l9 methane. 36 N ,N, ,N-tetra-(isopropyl)-4,4-diamino-dlphenyl 47 methane.

From the data in the above table, it will be seen that the tetra-ethyl derivative (run 34) was almost twice as effective as the corresponding tetra-methyl derivative (run 33) and that the tetra-isopropyl derivative (run 36) was more than twice as eflective as the corresponding tetra-npropyl derivative (run 35).

We claim as our invention:

1. A lubricant consisting essentially of an oil of lubri cating viscosity and a stabilizing concentration of an inhibitor selectedfrom the group consisting of 4,4'-di-(secalkylamino) diphenyl methane, N,N,N,N-tetra-(sec- 6. A lubricant consisting essentially of an oil of lubricating viscosity and a stabilizing concentration of N,N,N,N'-tetra-(sec-butyl)-4,4-diaminodiphenyl methane.

7. A lubricant consisting essentially of an oil of lubricating viscosity and a stabilizing concentration of N,N,N',N'-tetra-ethy1-4,4'-diaminodiphenyl methane.

8. A lubricant consisting essentially of an oil of lubricating viscosity and a stabilizing concentration of an inhibitor having both antioxidant and corrosion bearing inhibiting properties, said inhibitor being selected from the group consisting of 4,4'-di-(sec-alkylamino)-diphenyl methane, N,N,N',N'-tetra-(sec-alkyl) 4,4 diaminodiphenyl methane and N,N,N',N-tetra-ethyl-4,4-diamino- 1 1 diphenyl methane, said inhibitor being devoid of alkyl substituents in positions ortho to the nitrogen atoms.

9. A lubricant consisting essentially of a lubricating component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of an inhibitor selected from the group consisting of 4,4-di-(sec-alkylamino) -diphenyl methane, N,N,N,N- tetra-(sec-alkyl) 4,4 diaminodiphenyl methane and N,N,N',N-tetra-ethyl-4,4'-diaminodiphenyl methane.

1 0. The lubricant of claim '9 further characterized in that the lubricating component thereof is a grease comprising a lubricating oil and a metal soap of a higher fatty acid.

11. A lubricant consisting essentially of a lubricating component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of 4,4'-di-(isopropylamino)-diphenyl methane.

12. A lubricant consisting essentially of a lubricating component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of 4,4'-di-(sec-butylamino)-diphenyl methane.

13. A lubricant consisting essentially of a lubricating component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of N,N,N,N-tetra-(isopropyl)-4,4'-diaminodi- 25 phenyl methane.

14. A lubricant consisting essentially of a lubricating 12 component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of N,N,N',N'-tetra- (sec-butyl)-4,4'-diaminodiphenyl methane.

15. A lubricant consisting essentially of a lubricating component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of N,N,N,N'-tetra-ethyl-4,4'-diaminodiphenyl methane.

16. A lubricant consisting essentially of a lubricating component selected from the group consisting of greases and oils of lubricating viscosity, and a stabilizing concentration of an inhibitor having both antioxidant and corrosion bearing inhibiting properties, said inhibitor being selected from the group consisting of 4,4-di-(sec-alkylamino) -diphenyl methane, N,N,N',Ntetra-( sec-alkyl 4,4-diaminodiphenyl methane and N,N,N',N'-tetra-ethyl- 4,4-diaminodiphenyl methane, said inhibitor being devoid of alkyl substituents in positions ortho to the nitro gen atoms.

Sloan May 7, 1935 Kluge et al. Oct. 26, 1948 

9. A LUBRICANT CONSISTING ESSENTIALLY OF A LUBRICATING COMPONENT SELECTED FROM THE GROUP CONSISTING OF GREASES AND OILS OF LUBRICATING VISCOSITY, AND A STABILIZING CONCENTRATION OF AN INHIBITOR SELECTED FROM THE GROUP CONSISTING OF 4,4''-DI-(SEC-ALKYLAMINO)-DIPHENYL METHANE, N,N,N'',N''TETRA-(SEC-ALKYL)-4,4''-DIAMINODIPHENYL METHANE AND N,N,N'',N''-TETRA-ETHYL-4,4''-DIAMINODIPHENYL METHANE. 